Helping the New Hiker

[Raven]

FWIW, I used both together during some recent backcountry night skiing--the mapping GPS told me that I wanted to go SE from my current location to get to where I wanted to be and the compass told me which direction SE was.

Doug

Doug, just a clarification question as I'm not familiar, but do you mean to tell me a GPS cannot tell you which way north is? I would have thought they would have built in compasses at this point.

So much for assumptions.

 

[Kevin Rooney]

Doug, just a clarification question as I'm not familiar, but do you mean to tell me a GPS cannot tell you which way north is? I would have thought they would have built in compasses at this point.

So much for assumptions.

Am not Doug, nor did I sleep at that famous motel, but can answer your question -

A mapping GPS "knows" which way north is, but some models do not display a compass to show you where it is. Depends upon the feature set of the model you buy.

 

[sierra]

The compass and GPS tell you fundamentally different things: the compass gives you bearings while the GPS gives you your position (and 3-dimensional velocity and time). Maps enable one to find the relationships between the bearings and positions.

Modern mapping GPSes automate finding some of the relationships and presenting them to the user in a convenient way.

FWIW, I used both together during some recent backcountry night skiing--the mapping GPS told me that I wanted to go SE from my current location to get to where I wanted to be and the compass told me which direction SE was.

Doug

Thats interesting, I could see that being usefull on some of my CO trips , maybe Ill look into it when I go back west.

 

[DougPaul]

Doug, just a clarification question as I'm not familiar, but do you mean to tell me a GPS cannot tell you which way north is? I would have thought they would have built in compasses at this point.

Strictly speaking, a stationary GPS does not know which direction north is--it only knows were it (the GPS) is located*. However, if you move steadily in any direction, the GPS can infer your (3D) direction of movement from your changing location and your (3D) velocity (from Doppler shifting of the satellite signals) and can thus infer north.

* Strictly speaking a GPS only measures PVT: P=position (3D), V=velocity (=speed and direction, 3D), and T=time (1D) at any instant. Of course it can infer more from the sequence of positions--typical consumer GPSes produce one PVT estimate per second.

Many (eg Garmin 60CSx, 62S), but certainly not all (eg Garmin 60Cx), GPSes include a magnetic field sensor and can use it to determine magnetic north when stationary**. Since they also know where you are, they can apply the local declination (from a table or model) to show you true north. 3D sensors (eg in a 62s) are more accurate than 2D sensors (eg in a 60CSx) because they do not require that the GPS be held exactly level. The batteries in a GPS have magnetic fields and the currents flowing in the GPS wiring also produce magnetic fields so the compass must be recalibrated every time the batteries are changed or disturbed. Generally the magnetic sensor is used when stationary or at low speeds and the direction is taken from one's movement at higher speeds.

** There are GPS compasses that can determine direction without requiring motion, but they require multiple antennas fastened to a rigid structure (eg a boat superstructure or an airframe) and are not practical for hikers. They work by determining the differences in the locations of the antennas using DGPS (differential GPS).

Mechanical compasses are more accurate and do not require calibration (except, perhaps, for resetting the declination setting on compasses that have one) so I personally prefer to use them rather than the GPS magnetic compass when determining or sighting bearings. Mechanical compasses may also have sighting aids such as mirrors.

Additional info:
A GPS can determine the altitude directly, but the errors tend to vary on a short time scale (minutes) while the long-term average (hours) tends to be pretty accurate. Barometric altimeters tend to have small short-term errors and large long-term errors. Some GPSes include a barometric altimeter to get the best of both by using the GPS altitude to continuously calibrate the barometric altimeter. In effect the combination produces a continuously self-calibrating barometric altimeter. (GPS altimeter readings also tend to have 2x to 3x the error range of position--typ 95% probability of being within 20 or 30 meters compared to typ 95% probability of being with 10 meters for position.)

Doug

 

[DougPaul]

Thats interesting, I could see that being usefull on some of my CO trips , maybe Ill look into it when I go back west.

I bought my first GPS (a Garmin eTrex Vista loaded with US topo maps) shortly before a trip out west. I found it very helpful for solo navigation in the car (I put the day's route in the GPS the night before) as well as insurance for hiking. In one case, I used it to navigate a dirt road for which I had text descriptions and a GPS map, but not shown on my paper maps. The GPS track told me that I was going in the expected direction and would allow me to backtrack if necessary. I probably wouldn't have tried it without the GPS. (Burr Trail Rd and Notom-Bullfrog Roads, Capitol Reef NP) And yes, I was able to get the proper paper topo map the next day...

Note: many hiking GPSes work very well for car navigation, too. Just get a 12V power cord to save your batteries on long trips. (The backlight, in particular, is pretty power hungry.)

Suggestion:
If you get a GPS prior to a big trip, make sure that you allow enough time to learn to use it before going--some of the details can be complicated and/or tricky.

Doug

 

[RoySwkr]

A mapping GPS "knows" which way north is, but some models do not display a compass to show you where it is.

And you may not need to know where North is.

My sister (who would carry her Garmin when mapping with a backpack Trimble because the Garmin was better for navigation) never used the arrow screen and felt it was superfluous. The map screen has a pointer showing where you are, and the direction you are going if you are moving. You really don't care about the numeric value of your heading, only whether the dot marking your location is getting closer to your next waypoint and/or following your proposed road/trail if shown on the map.

 

[Kevin Rooney]

And you may not need to know where North is.

My sister (who would carry her Garmin when mapping with a backpack Trimble because the Garmin was better for navigation) never used the arrow screen and felt it was superfluous. The map screen has a pointer showing where you are, and the direction you are going if you are moving. You really don't care about the numeric value of your heading, only whether the dot marking your location is getting closer to your next waypoint and/or following your proposed road/trail if shown on the map.

That's a good point, Roy. Whether you refer to the compass on a mapping GPS such as the 60CSx and its replacement series is probably an individual thing. Like your sister, I rarely use the compass on mine. About the only time I do is if I'm in a group, and someone asks what direction a certain feature is and rather than give a general answer like "It's East of us" I give them a more precise answer, like ESE after glancing at the GPS.

When I'm using my GPS as a navigational aid, I'm watching the little triangle which indicates direction of travel, as the absolute direction of travel is of little practical use for this type of navigation. That statement may be difficult for someone who has never used a GPS to follow, and hopefully no one will insist I learn how to use a compass. (If anyone should feel so compelled - I am competent with a compass, and have taught map and compass skills.)

 

[DougPaul]

My sister (who would carry her Garmin when mapping with a backpack Trimble because the Garmin was better for navigation) never used the arrow screen and felt it was superfluous.

Trimble makes survey GPSes--far to expensive for most hikers. Garmin makes consumer GPSes (along with aeronautical and marine GPSes) all of which are aimed toward navigation.

And you may not need to know where North is.

The map screen has a pointer showing where you are, and the direction you are going if you are moving. You really don't care about the numeric value of your heading, only whether the dot marking your location is getting closer to your next waypoint and/or following your proposed road/trail if shown on the map.

Agreed.

We should also note that Garmin (and presumably many other consumer GPSes) have two map display orientation modes:
* In "North Up" mode, the map is always displayed North up and the pointer is in your current location and pointed in the direction that you are moving. There is, of course, no need to indicate which direction North is...
* In "Track Up" mode, the map is rotated around your current location so that your direction of travel (and the pointer) is always up. The GPS displays an "N" arrow in the corner of the display.

In both cases, the GPS knows where north is.

IMO, the North Up display is a navigator's display and the Track Up display is intended to show the view out the front windscreen.

Personally, I always use the North Up mode--I find the spinning map of the Track Up display disorienting. (Others may differ. FWIW, I also hold my paper maps North up too...)

I rarely use numerical bearings except to transfer them between my GPS (or map) and my compass. Also, one can often determine an approximate bearing by comparing the recorded track on the GPS and the direction of interest.

Doug

 

[NewHampshire]

My eating strategy: Carbs before and during the hike, and protein after.

I am somewhat similar. I have a good size breakfast of complex carbs (important note...COMPLEX CARBS) before leaving the house. The drive of about 1 1/2-3 1/2 hours (depending on where I am going that day) gives plenty of time to get the complex carbs into the system. I then top off with simple carbs (sugars mostly) throughout the hike occasionally adding more complex carbs (in the form of a big fat dill pickle...YUM! ). Afterwards it is usually a nice meal with plenty of meat involved.

Brian